The present disclosure relates to the subject matter contained in Japanese Patent Application No. 054752/2005 filed on Feb. 28, 2005, which is expressly incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a steam barrier film and, more specifically, it relates to a laminate type steam barrier film suitable to substrates for various kinds of devices and coating films for the devices. Further, the invention also relates to a substrate for use in image display devices and organic EL devices excellent in durability and flexibility and, more particularly, relates to a substrate excellent in handleability with no electrostatic troubles.
2. Description of the Related Art
Gas barrier films in which thin films of metal oxide such as aluminum oxide, magnesium oxide, and silicon oxides are formed on the surfaces of plastic substrates or films have been generally used so far for packaging of articles requiring shielding of steams or various gases such as oxygen, or packaging application for preventing denaturation of foodstuffs, industrial products, and medicines. Further, the gas barrier films have also been started for use in substrates of liquid crystal display devices, solar cells or electroluminescence (EL) devices in addition to the packaging use. Particularly, in transparent substrates which have been applied progressively to liquid crystal display devices, EL devices, etc., high level of demands such as long time reliability, high degree of freedom in view of shape, and capability of display on a curved surface have been required in addition to the demand for reduction in the weight and increase in the size.
Recently, in the field of the liquid crystal display devices, the EL devices, etc., film substrates such as those made of transparent plastics are being used instead of glass substrates, which are heavy, have a tendency to crack and present difficulties in increasing the area. Further, since the plastic substrates such as made of transparent plastics can not only cope with the requirements described above but also can be applicable to the roll-to-roll system, they are advantageous over glass materials in view of the productivity and the reduction of cost. However, film substrates such as of transparent plastics involve a problem of poor gas barrier properties in comparison with glass. Since steam or air permeates in a case of a substrate of poor gas barrier property, when it is used for example on a liquid crystal display device, liquid crystals in a liquid crystal cell are deteriorated and deteriorated portions result in display defects that deteriorate the display quality.
For solving such problems, it has been known to form a thin film of a metal oxide on the film substrate described above, and use the gas barrier film as a transparent substrate. As gas barrier films used for packaging materials and liquid crystal display devices, those formed by vapor depositing silicon oxide on a plastic film (for example, in JP-B-53-12953 (p1 to p3) (Patent Document 1) and those formed by vapor depositing aluminum oxide (for example, in JP-A-58-21734 (p1 to p4) (Patent Document 2)) are known and they have a steam barrier property of about 1 g/m2/day. However, the steam barrier property as low as about 0.1 g/m2/day has been demanded recently for the film substrate along with increase in the size of liquid crystal displays or development for highly fine displays.
Further, most recently, development has been progressed, for example, in organic EL displays or highly fine color liquid crystal displays requiring further higher barrier property and it has been demanded for a substrate having a performance of higher barrier property, particularly, a steam barrier property of less than 0.1 g/m2/day while maintaining transparency usable therein. For coping with such a demand, films deposition by way of a sputtering method or a CVD method of forming a thin film using plasmas generated by glow discharge under low pressure conditions have been studied as means capable of expecting highly barrier performance. Further, it has been proposed a technique of preparing a barrier film having an alternate lamination structure of organic layer/inorganic layer by a vacuum vapor deposition method (for example, refer to U.S. Pat. No. 6,413,645B1 (p4, [2-54] to p8, [8-22]) (Patent Document 3) and “Thin Solid films” written by Affinito, et al., (1996), p. 290 to 291 (p63 to p67) (Non-Patent Document 1)).
On the other hand, it has also been disclosed a technique of not only inhibiting intrusion of steams from the outside but also positively capturing water by forming a film of a moisture absorbent to the inner lateral surface of a sealing member (refer, for example, to JP-A-2000-260562 (p3 to p5) (Patent Document 4)). However, since the barrier performance of the sealant or the substrate is still insufficient also in such techniques, they give rise to a problem of causing film deformation by moisture absorption after lapse of long time to result in fetal deterioration of image quality as displays. Further, they also involve a problem that metal ions forming the hygroscopic layer diffuse during device manufacturing steps or during use to deteriorate the performance and, in this sense, it has been desired for the development of a technique capable of compatibilizing transparently and high hygroscopic performance and high barrier performance.
Further, problems in such substrates also include deposition of dusts caused in the course of manufacture which worsen the substrate performance (barrier property). Further, they also give rise to a problem that not only dusts are deposited due to electrostatic charges during handling of the substrate but also generation of electrostatic troubles to the substrates by the generation of static electricity to bring about troubles in view of the characteristics. Further, highly heat resistance substrates developed in recent years involve the problem in view of the cost for the substrate film, which results in remarkable hindrance in the provision of actual commercial products. Accordingly, there has been a demand for steam barrier films capable of using substrate films at a low cost and favorable in the handleability.